Turbine blade positioning and gaging fixture

ABSTRACT

A jig and gaging fixture providing determination of acceptable and nonacceptable turbine blades, particularly nozzle vanes, and precision positioning of the same between a pair of concentric shrouds in a single operation.

[451 Jan.25, 1972 United States Patent Stahl [56] References Cited UNITED STATES PATENTS [54] TURBINE BLADE POSITIONING AND GAGING FIXTURE 3,246,389 4/l966 Pfau......................................29/200.I 3,414,958 l2/l968 Anderson.........................,....29/200J Assignee:

[22] Filed:

Primary Examiner Frank T. Yost Attorney-Raymond P. Wallace and Victor D. Behn [21] Appl. No.:

ABSTRACT [52] 0.8. CI.

W323, 19/00 A jig and gaging fixture providing determination of acceptable .29/200J, 200 P [5i] Int.Cl..............

Fieldoi and nonacceplable turbine blades, particularly nozzle s,

and precision positioning of the same between a pair of concentric shrouds in a single operation.

6 Claims, 8 Drawing Figures PATENTED m5 1972 Sam 1 er 3 FIG 1 FIG..3

[.N'VliA'MR FREDERICK J.STAHL AGENT PATENTEDJMWZ sleaasos SHEEI 2 OF 3 [LT 1F.

FREDERICK J. STAHL YRWPWJLM,

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FREDERICK J. STAHL WW Walaw AGENT BACKGROUND OF THE INVENTION This invention pertains to gas turbine engines, and more particularly to a method and apparatus for gaging, assembling, and positioning turbine blades in supporting structures.

Turbine stator vanes are commonly assembled in a generally radial pattern between inner and outer shrouds. The geometric flow area is the total open space through which gas can flow, and is the sum of the areas of the blade throats, the most restricted portions of the passages between the blades. The geometric flow area may be very precisely specified within small tolerances, and particularly so in small gas turbines, since the performance of the engine depends on the proper flow of gas to the rotor blades. Not only must the total flow area be within tolerance, but also the flow area of any individual throat, and the sum of the throat areas within some specified angular section of the nozzle, in order that no portion of the gas flow to the rotor may vary markedly from another and thus produce unequal loading of the turbine rotor. It is obvious that with a small tolerance on the total flow area, any component of the total sum, such as sectorial tolerances and the tolerances of individual throats, must be very small indeed, and the positioning of the blades must achieve high precision.

It has been the practice in the prior art to construct such an assembly by positioning the blades individually and successively, tack-welding each in place as the operation preceded. Although by this method no individual throat might exceed its tolerance, the accumulation of tolerances around the circumference might severely unbalance some portion of the stator, requiring a more or less complete rework after the assembly is completed. The present invention obviates such a costly and time-comsuming operation, has entirely eliminated rework, and results in a better control of the final product.

SUMMARY This invention provides a gaging tool of annular configuration capable of holding inner and outer shrouds firmly in concentric relationship, the shrouds being keyed to the tool with the inner and outer blade seats properly aligned. The gaging fixture carries a plurality of retractable, shouldered gage pins equal in number to the number of the blades and positioned circumferentially of the fixture approximately midway of the blade span, with the pin axes parallel to the shroud axes. The blades are positioned in their shroud seats with the trailing edge of each blade resting in the angle formed by the reduction of the diameter of the gage pin at the shoulder. Since the width of the throat of each blade passage is the normal from the convex surface of one blade to the trailing edge of the adjacent blade, the throat widths are now precisely established. The blades are then firmly held in place by a clamping ring bearing against their leading edges, and tack welded to the inner and outer shroud rings at the blade seats, after which the complete assembly may be furnace brazed.

If any blade should have too great a cord width or an improper curvature it will not clear its gage pin when positioned in the shrouds seats, and may be rejected. If its cord width is too narrow the clamping ring will not contact the leading edge and the blade will be loose in its shroud seats, whereupon again it may be rejected before further operations. However, before rejecting any blade for improper fit, a master gaging blade is tried in the corresponding blade seats, and if it does not pass the gage pin and seat properly in the shrouds there is indicated a defeat in either or both the shrouds.

It is therefore an object of this invention to provide a tool for properly positioning turbine blades in supporting structures.

It is another object to provide a fixture for precision control of interblade passages in a turbine structure.

It is a further object to provide a fixture for precision control of the geometric flow area of a turbine structure.

Other objects and advantages will become apparent on reading the following specification in connection with the annexed drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a semischematic perspective view of a turbine stator;

FIG. 2 is a plan view of a portion of the gaging fixture, with a fragmentary representation of a pair of concentric shrouds with blades installed;

FIG. 3 is a fragmentary section taken on line 3-3 of FIG. 2, with a blade partially inserted into the assembly;

FIG. 4 is a fragmentary section taken on line 44 of FIG. 2;

FIG. 5 is an elevation of the gaging fixture at an advanced stage of the assembly;

FIG. 6 is a s semischematic representation of a stage of assembly; and

, FIG. 7A and 7B are diagrammatic representations of a means of adjusting the dimension of the interblade throats.

DESCRIPTION OF A PREFERRED EMBODIMENT In FIG. 1 there is shown semischematically a turbine stator 1 1 of the general type contemplated for assembly by means of the gaging fixture of this invention. The stator comprises an inner shroud ring 12, and an outer flanged shroud ring 13 with a plurality of blades 14 being positioned by the rings and fixed thereto. The outer shroud 13 is provided with holes 16 of generally airfoil configuration, through which the blades are inserted at assembly. The inner shroud is provided with holes 17 in which the root end of the blade is seated, but holes 17 are not of full airfoil configuration, stopping short of the trailing edge with a square end. The root ends of the blade (best shown in FIG. 3) are shouldered 18 at the trailing edge conformably to holes 17, which provides the blade with a stop against the inner shroud.

FIG. 2 shows a plan view of certain portions of a positioning and gaging fixture 19 for assembling turbine stators and rotors of the type described above.

There is provided an annular platform 21 resting on legs 22. Extending from the upper surface of the platform is a raised annular portion 23 having its outer circumference an exact fit to the inner dimension of the outer s shroud member 13. The platform 21 bears a key 24 having a tongue which fits into a notch in the flange of the outer shroud for proper azimuthal positioning. The inner circumference of raised portion 23 is an exact fit to the outer dimension of inner shroud l2, and there is a second key 26 fitting into a notch in the edge of the inner shroud holding it in position so that the blade seats of the two shrouds will be suitably aligned. The keying means for the shrouds need not be exactly those shown; there may be used any suitable keying means aligning the two shrouds in proper relation.

Platform 21 is provided with pivotable dogs 27 for clamping the flange of the outer shroud flat to the platform. The inner shroud seats on a shoulder of the platform at the inner circumference of portion 23, and a plurality of arcuate clamping segments 28 are provided to hold it firmly in place, as by bolts 29 or other appropriate fasteners. In FIG. 2 one of the segments 28 is shown clamping a fragmentary showing of the inner shroud, and two other segments are shown in the retracted position.

A number of vanes 14 are shown mounted in the portion of the shrouds depicted in FIG. 2, looking down on their leading edges. Their trailing edges, at approximately midspan, rest on gage pins 31 (better shown in FIG. 4) in the angle formed by the reduction of the diameter of the upper end of the pin.

In FIG. 3 there is shown the means of positioning and adjusting the blades. A blade 14 is inserted through the aperture 16 in the outer shroud 13 and pushed through until its root end seats in the aperture 17 in the inner shroud with the shoulder 18 at the trailing edge of the root against the surface of the inner shroud. Since in many turbine devices of this type the blade span is not exactly radial from the axis of the device, if pins 31 were permanently fixed in their gaging position the blades would not pass the pins when inserted at an angle to the radius. For this reason, the gaging pins are made retractable to take them out of the path of blade insertion. The base of pin 31 travels in a bore 32 through platform 21, impelled by a thumbscrew 33 or other suitable means. The bore 32 is necked down at its upper end to a diameter allowing clearance for the portion of the pin which travels into the area of the blade span, thus providing a shoulder 34- against which the larger diameter of the pin will set when fully inserted. The position of the shoulder in the bore and the length of the pin above its base are mutually selected so that the pin when fully inserted seats at the exact height to receive the trailing edge of the blade in the angle formed by the reduced diameter of the upper end of the pin.

FIG. shows the next stage of assembly. After a full complement of blades has been inserted in the two shrouds a clamping ring 36 is applied against the exposed leading edges of the vanes 14 and attached to a convenient portion of the fixture, as by screws 37, to hold the vanes firmly in place. The result of the action is indicated schematically in FIG. 6. The airfoil-shaped vane slots l6, 17 (indicated by dotted line) in the outer and inner shrouds respectively have been made slightly oversized so that the vanes may be easily inserted. The amount of clearance need not be more than some thousandths of an inch, but has been exaggerated in the drawing for clarity. The position of the trailing edges of the blades is firmly established by their seating on the shoulders of gaging pins 31, as is the dimension of the throat of the interblade passages, indicated by the arrow T at the normal from the convex surface of a blade to the trailing edge of the adjacent blade. The pressure of clamping ring 36 tilts all the blades slightly in the direction of their convex sides without altering the position of the trailing edges or changing the dimension of the blade throats. This tilt is restrained by the convex side of the blades near the leading edge coming into contact with the edge of the blade slots, which serves as a limit, and the entire ring of blades is now firmly held. Thereupon, tack welds are made at each end of the blade between the blade and the shrouds, preferably at points where the blade touches or closely approaches the edge of the slot, as indicated by x and y in FIG. 6. The tack welds at the root ends of the blades are made on the inner circumference of the inner shroud, and those at the tip ends are made on the outer circumference of the outer shroud, in order that no weld deposit should interfere with the geometric flow area. After the tack welds are made the device is removed from the fixture and the blades are fully brazed into their slots.

It is sometimes desired to have a turbine engine run hotter or cooler than the nominal parameter of heat flow. Within a given design, opening the interblade throats slightly increases the geometric flow area and causes the engine to run cooler. Similarly, slightly closing the throats decreases the geometric flow area, resulting in hotter running. The amount of adjustment made for the desired change may be very slight, as from one to a few thousandths of an inch change in the dimension of the throats.

FIGS. 7A and 7B show diagrammatically a means of adjusting the throat dimension, using the fixture described above with only a change of gaging pins. Since the actual adjustment is minute, it has been greatly exaggerated in the drawings for clarity of illustration. In FIG. 7A there are shown centerlines 14a which represent the tilt angle of the blades in their shroud seats, at a higher degree of tiltthan that previously described.

This is achieved by the use of gaging pins 31a, wherein the small diameter of the top portion of the pin is reduced still further, and the shoulder portion is raised higher than that of the previous embodiment. These changes result in raising the trailing edge of the blade to produce a greater degree of tilt, and thus close the interblade throats to the value indicated by the arrow Ta.

In FIG. 7B are shown centerlines 1412 representing the angle of blades at a lesser degree of tilt. This is accomplished by using gaging pins 31b, in which the diameter of the upper portion of the pin is increased, and the shoulder is dropped, resulting in lowering the trailing edge of the blade and reducing the tilt to a lesser degree, thus opening the throats to the value indicated by the arrow Tb. It is emphasized that although the changes shown in the drawings are considerable, the actual variations in the diameter of the upper part of the pin and the height of its shoulder are of the order of thousandths of an inch.

From the foregoing description it will be seen that very precise control may be exercised over the dimension of the geometric flow area of each interblade passage, of the total flow area, and of any selected segment thereof.

What is claimed is:

1. A fixture for precision assembly of a turbine structure having a pair of concentric shroud structures each havinga plurality of blade seats with a plurality of blades disposed generally radially therebetween, the fixture comprising in combination means for holding the shrouds in coaxial and radial alignment with the inner and outer blade seats in proper relationship, the holding means having means receiving the trailing edge of each blade and precisely positioning the same with respect to the trailing edges of adjacent blades tocontrol the dimension of interblade throats, and clamping means holding the blades firmly in their seats and against the trailing edge positioning means, the shroud holding means being an annular structure having on its inner circumference a shoulder receiving one end of the inner shroud and on its outer circumference a shoulder receiving one end of the outer shroud, keying means positioning the inner and outer shrouds with their blade seats in proper mutual relationship, and clamping means holding the inner and outer shrouds firmly in fixed position.

2. A fixture as recited in claim 1, wherein the trailing edge positioning means comprises a plurality of gaging pins equal in number to the number of blades, the pins protruding into the blade region between the shrouds, each pin having on its protruding end a reduced diameter providing a shoulder receiving the trailing edge of its associated blade.

3. A fixture as recited in claim 2, wherein the pins are retractable to allow passage of blade trailing edges before seating.

4. A fixture as recited in claim 3, wherein the pins are replaceable with pins of different reduced diameter and different shoulder height to allow assembly of turbine structures having different interblade throat dimensions.

5. A fixture as recited in claim 2, wherein the gaging pins are circumferentially positioned in the fixture to protrude into the blade region approximately midway of the blade span between the shrouds.

6. A fixture as recited in claim 2, wherein the blade clamping means is an annular member bearing against the leading edges of the blades holding the trailing edges firmly seated against the gaging pin shoulders and tilting the leading edges toward the convex sides of the blades against a portion of the blade seats. 

1. A fixture for precision assembly of a turbine structure having a pair of concentric shroud structures each having a plurality of blade seats with a plurality of blades disposed generally radially therebetween, the fixture comprising in combination means for holding the shrouds in coaxial and radial alignment with the inner and outer blade seats in proper relationship, the holding means having means receiving the trailing edge of each blade and precisely positioning the same with respect to the trailing edges of adjacent blades to control the dimension of interblade throats, and clamping means holding the blades firmly in their seats and against the trailing edge positioning means, the shroud holding means being an annular structure having on its inner circumference a shoulder receiving one end of the inner shroud and on its outer circumference a shoulder receiving one end of the outer shroud, keying means positioning the inner and outer shrouds with their blade seats in proper mutual relationship, and clamping means holding the inner and outer shrouds firmly in fixed position.
 2. A fixture as recited in claim 1, wherein the trailing edge positioning means comprises a plurality of gaging pins equal in number to the number of blades, the pins protruding into the blade region between the shrouds, each pin having on its protruding end a reduced diameter providing a shoulder receiving the trailing edge of its associated blade.
 3. A fixture as recited in claim 2, wherein the pins are retractable to allow passage of blade trailing edges before seating.
 4. A fixture as recited in claim 3, wherein the pins are replaceable with pins of different reduced diameter and different shoulder height to allow assembly of turbine structures having different interblade throat dimensions.
 5. A fixture as recited in claim 2, wherein the gaging pins are circumferentially positioned in the fixture to protrude into the blade region approximately midway of the blade span between the shrouds.
 6. A fixture as recited in claim 2, wherein the blade clamping means is an annular member bearing against the leading edges of the blades holding the trailing edges firmly seated against the gaging pin shoulders and tilting the leading edGes toward the convex sides of the blades against a portion of the blade seats. 